(1) Field of the Invention
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of reducing the number of particles formed on a wafer during PE-silane oxide film formation in the fabrication of integrated circuits.
(2) Description of the Prior Art
Silicon oxide films are widely used in semiconductor processing as interlevel and intermetal dielectrics. Silicon oxide films are often formed by plasma-enhanced chemical vapor deposition (PECVD). FIG. 1 illustrates a typical CVD chamber 20. The wafer is placed into the chamber. Gases are flowed into the chamber whereby the silicon oxide film is formed on the surface of the wafer. Typically, silane (SiH4) is flowed from the Mass Flow Controller (MFC) of one gas inlet 22 while N2O is flowed from the MFC of a second gas inlet 24. The reaction of the two gases forms SiO2.
In the typical silicon oxide PE-silane reaction, the SiH4 and N2O gases are flowed into the CVD chamber with no radio frequency power as a stabilization step. Then the radio frequency, for example 280 watts, is applied while the two gases continue to flow to form the silicon oxide film.
After the silicon oxide film was formed according to the conventional recipe, the inventors obtained a particle count on the wafer. Unexpectedly, they found an extremely high particle count of more than 20,000 particles of a size 0.2 xcexcm and larger. It is desirable to find a method of forming a silicon oxide film without this extremely high particle count.
U.S. Pat. No. 5,279,865 to Chebi et al teaches a method of forming a silicon oxide layer using silane flow. U.S. Pat. No. 5,525,550 to Kato teaches a method of forming silicon oxide by CVD using silane and water as the main feed gases. U.S. Pat. No. 5,576,076 to Slootman et al teaches forming an silicon dioxide layer by subjecting a wafer to an electrical discharge in the presence of silane and N2O. U.S. Pat. No. 5,214,952 to Leggett et al teaches the use of a series of highly accurate mass flow controllers to deliver a high purity calibration gas mixture to a gas analyzer. None of these references address the particle problem.
Accordingly, it is a primary object of the invention to provide a process for greatly reducing the particle count in the formation of a PE-silane oxide film.
In accordance with the object of the invention, a method of forming a PE-silane oxide layer with a greatly reduced particle count is achieved. A semiconductor substrate is provided over which a silicon oxide film is to be formed. The silicon oxide film is formed by the steps of: 1) pre-flowing a non-silane gas into a deposition chamber for at least two seconds whereby the pre-flowing step prevents formation of particles on the silicon oxide film, and 2) thereafter depositing a silicon oxide film by chemical vapor deposition by flowing a silane gas into the deposition chamber to complete formation of a silicon oxide film using plasma-enhanced chemical vapor deposition in the fabrication of an integrated circuit.